The present invention relates to a method for high speed machining of metallic work pieces and a coated cemented carbide cutting inserts particularly useful for that application.
Cemented carbide cutting tools coated with various types of hard layers have been commercially available for years. Such tool coatings are generally built up by one Ti(C,N) hard layer and one Al2O3 hard layer where the Ti(C,N) is the innermost layer adjacent to the cemented carbide. The thickness of the individual layers is carefully chosen to suit different cutting applications and work-piece materials e g cast iron and stainless steel. More particularly, a coating generally comprises:                a Ti-compound layer, as an inner layer, formed by CVD or MT-CVD with an average thickness of 2 to 10 μm made of one major Ti(C,N) layer or a plurality of two or more layers of TiC, TiN, Ti(C,N), Ti(C,O) and Ti(C,N,O)        an Al2O3-layer, as an outer layer formed by CVD which has an average thickness of 2 to 10 μm and generally with the α- and/or κ type crystal structure;        optionally, a TiN layer having an average thickness of 0.5 to 2 μm, as a surface layer, deposited on the upper layer for the purpose of identification of the cutting edges before and after cutting operations because of its golden color tone.        
Such coated cemented carbide tool inserts may be used for both continuous and interrupted cutting operations of various types of steels and cast iron.
U.S. Pat. No. 6,733,874 discloses a cutting tool used for machining operations at cutting speed up to 420 m/min, having a hard coating including: a Ti compound layer, as a lower layer, formed by vapor deposition, having an average thickness of 0.5 to 20 μm and made of at least one layer chosen from TiC, TiN, Ti(C,N), Ti(C,O) and Ti(C,N,O); an aluminium oxide layer, as an intermediate layer, with an average thickness of 1 to 25 μm and a heat transformed α-type crystal structure derived from a vapor deposited κ- or θ-type aluminium oxide layer, and with a structure having cracks therein formed during heat transformation uniformly dispersed and an aluminium oxide layer, as an upper layer, formed by vapor deposition having an average thickness of 0.3 to 10 μm and an (α-type crystal structure.
U.S. Pat. No. 6,720,095 discloses a coated sintered cemented carbide body including a cemented carbide body, a first layer adjacent the cemented carbide body, the first layer including Ti(C,N) and having a thickness of from about 3 to about 20 μm, an alumina layer adjacent said first layer, the alumina layer including α-Al2O3 or κ-Al2O3 and having a thickness of from about 1 to about 15 μm, and a further layer adjacent the alumina layer of a carbide, carbonitride or carboxynitride of one or more of Ti, Zr and Hf, the further layer having a thickness of from about 1 to 15 μm. A friction-reducing layer, including one or more of γ-Al2O3, κ-Al2O3 and nanocrystalline Ti(C,N) and having a thickness of from about 1 to about 5 μm, can be adjacent to the further layer.
U.S. Pat. No. 6,183,846 discloses a coated cutting tool including a hard coating on a surface of a base material of cemented carbide or cermet. The hard coating includes an inner layer on the base material, an intermediate layer on the inner layer and an outer layer on the intermediate layer. The inner layer with a thickness of 0.1 to 5 μm consists of a carbide, a nitride, a carbonitride, a carbooxide, a carbo-oxynitride or a boronitride of Ti. The intermediate layer consists of Al2O3 with a thickness of 5 to 50 μm or ZrO2 with a thickness of 0.5 to 20 μm. The outer layer with a thickness of 5 to 100 μm consists of a carbide, a nitride, a carbonitride, a carbo-oxide, a carbo-oxynitride or a boronitride of Ti.
Cemented carbide, in particular coated cemented carbide, is by far the most commonly used cutting tool material. Other materials include cermets, ceramics, cBN and diamond. Ceramics are often used in applications requiring high productivity such as the machining of brake discs and other components in the car industry because cemented carbide can not withstand the high temperature generated during the high speed operations required to obtain the desired high productivity. However, ceramic tools are expensive because of the high manufacturing cost. It is therefore a desire, if possible, to be able to replace ceramic tools with cemented carbide tools.